It has been found that one of the major sources of inefficiency in heating furnaces is heat loss through the furnace flue during periods when no combustion is taking place in the furnace. Automatic damper assemblies for opening and closing a flue in accordance with the combustion state of a furnace or fireplace are well known in the art. Prior art damper systems, however, have been relatively complex and expensive. Examples of prior art automatic damper assemblies are described in U.S. Pat. Nos. 1,773,585 issued to Klockau on Aug. 19, 1930, 1,927,670 issued to Morrow on Sept. 19, 1933, 2,053,750 issued to Terry on Sept. 8, 1936, 2,117,787 issued to Bock on May 17, 1938, 2,130,491 issued to Gilliland on Sept. 20, 1938, 2,154,644 issued to Sweatt on Apr. 18, 1939, 2,155,642 issued to Dewey on Apr. 25, 1939, 2,165,488 issued to Klimis on July 11, 1939, 2,224,705 issued to Stringer on Dec. 10, 1940. 2,226,081 issued to Stuart on Dec. 24, 1940, 2,243,715 issued to Miller on May 27, 1941, 2,381,437 issued to Crew et al on Aug. 7, 1945, 2,446,834 issued to Kaufman on Aug. 10, 1948, 2,508,885 issued on Mackay on May 23, 1950, 2,692,640 issued to Field on Oct. 26, 1954, 2,856,992 issued to Bartels on Oct. 21, 1958, 3,010,451 issued to Hodgins on Nov. 28, 1961, 3,580,238 issued to Diehl on May 25, 1971, 3,773,028 issued to Schreibeis on Nov. 20, 1973, 4,005,820 issued to Cress on Feb. 1, 1977.
The present invention provides a simple and inexpensive damper assembly for controllably closing the flue of electrically ignited furnace. A damper is rotatably mounted within the flue, and cooperates with a linkage assembly including a first linkage arm pivotally mounted and biased against a motor driven cam such that the position of the linkage arm changes in accordance with rotation of the cam. Control signals are generated to the motor to effect rotation of the cam in accordance with the combustion state of the furnace.
More specifically, burner control signals to the furnace burner indicating a demand for combustion activate a relay in the damper assembly. A switch, cooperating with the cam, completes a current path to the motor from the normally closed (unactivated) set of relay contacts when the damper is in other than a closed position. Another switch cooperating with the linkage assembly, completes a current path from the normally open set of relay contacts (closed when activated) to the motor when the damper is in other than open position, and when the damper is in the open position completes a current path from the normally open set of contacts to the furnace burner to enable combustion.
The damper assembly is contained in a unitary module, for each installation into an existing furnace flue and control system. Further, it should be appreciated, that the second switch provides an interlock system, which prevents combustion in furnace unless the damper assembly is fully opened. Further, the use of the cam-linkage mechanism for rotating the damper provides an inherent delay during which the gases remaining from combustion, even after the combustion itself has ceased, are purged (allowed to escape), thus alleviating the rather complex delay mechanisms utilized in the prior art systems.